Datasheet

Data Sheet
©2013
Würth Elektronik eiSos GmbH & Co. KG - REV 0.2
PRELIMINARY
10/ 25
171032401/WPMDH1302401J
MagI³C Power Module Product Family
VDRM - Variable Step Down Regulator Module
J CIRCUIT DESCRIPTION
MagI³C 7 Steps to design the power application
The next 7 simple steps will show how to select the external components to design your power application:
1. Program under voltage lockout divider
2. Program output voltage
3. Select soft-start capacitor
4. Select output capacitor
5. Select input capacitor
6. Set operating frequency with R
ON
7. Select feed forward capacitor
R
ON
C
IN
V
IN
RON
VIN
EN AGND SS
FB
VOUT
Module
R
ENT
R
ENB
R
FBT
R
FBB
C
SS
C
FF
C
OUT
V
OUT
Step 1. Select Enable Divider, R
ENT
, R
ENB
The enable input provides a precise 1.18V reference threshold to allow direct logic drive or connection to a voltage
divider from a higher enable voltage such as V
IN
. The enable input also incorporates 90mV (typ) of hysteresis
resulting in a falling threshold of 1.09V. The maximum recommended voltage into the EN pin is 6.5V. For applications
where the midpoint of the enable divider exceeds 6.5V, a small zener can be added to limit this voltage.
The function of the R
ENT
and R
ENB
divider shown in the application block diagram is to allow the designer to choose
an input voltage below which the circuit will be disabled. This implements the feature of programmable under voltage
lockout. This is often used in battery powered systems to prevent deep discharge of the system battery. It is also
useful in system designs for sequencing of output rails or to prevent early turn-on of the supply as the main input
voltage rail rises at power-up. Applying the enable divider to the main input rail is often done in the case of higher
input voltage systems such as 24V AC/DC systems where a lower boundary of operation should be established. In
the case of sequencing supplies, the divider is connected to a rail that becomes active earlier in the power-up cycle
than the MagI³C power module output rail. The two resistors should be chosen based on the following ratio:









(1)
The EN pin is internally pulled up to V
IN
and can be left floating for always-on operation. However, it is good practice
to use the enable divider and turn on the regulator when V
IN
is close to reaching its nominal value. This will guarantee
smooth startup and will prevent overloading the input supply.
Step 2. Select Output Voltage (V
OUT
)
Output voltage is determined by a divider of two resistors connected between V
OUT
and ground. The midpoint of the
divider is connected to the FB input. The voltage at FB is compared to a 0.8V internal reference. In normal operation
an on-time cycle is initiated when the voltage on the FB pin falls below 0.8V. The high-side MOSFET on-time cycle
1.
2.
3.
4.
5.
6.
7.